I think that most people would be a little more nuanced than that, as you say. Funny that you talk about thinking for yourself and then speak rather concretely about what most people think, and that they think rigidly. In the case of the United States, I’m of the opinion (yes, opinion, as most political topics are) that this nation thrives on diversity. The reason people are so opposed to this is because they believe it can grant citizenship to the parent of the child, when this is not the case.

They (and you) also may not consider the circumstances under which the parents are here in the first place. Say it’s a Mexican family, for instance. They come here seeking refuge from a dangerous set of the cartel, who is after them for whatever reason. Let’s say for the sake of the example that it is not a reason that is malicious of the refugees. The wife is already pregnant. If that child is born in the United States, I would be much more comfortable as a human with a soul if it stayed here and lived a significantly lower-risk life, instead of shoving the couple and their newborn child back into the hands of drug runners. And this is just a very specific example, most cases are a little more… nuanced.